1. Field of Invention
The present invention relates to a method of manufacturing dynamic random access memory (DRAM). More particularly, the present invention relates to a method of planarizing the peripheral circuit region of advanced DRAM.
2. Description of Related Art
FIGS. 1A through 1G are schematic cross-sectional views showing the progression of steps for producing a conventional crown-shaped capacitor in 0.21/0.18 xcexcm DRAM. First, as shown in FIG. 1A, a silicon oxide layer 101 and a silicon nitride layer 102 are sequentially formed over a substrate 100. After polysilicon plugs 104 are formed in the silicon nitride layer 102 and the silicon oxide layer 101, a patterned silicon oxide layer 106 is formed over the silicon nitride layer 102. As shown in FIG. 1B, a conformal doped amorphous silicon layer 108 is formed over the exposed silicon nitride layer 102 and the silicon oxide layer in the crown-shaped capacitor region 120. The doped amorphous silicon layer 108 also covers the silicon oxide layer 106 in the peripheral circuit region 122. As shown in FIG. 1C, a photo resist (PR) layer 110 is formed filling the crown-shaped capacitor region 120 and the peripheral circuit region 122. The PR layer 110 protects a portion of the doped amorphous silicon layer 108 in a subsequent operation. As shown in FIG. 1D, chemical-mechanical polishing is carried out to polish the PR layer 110 and to remove a portion of the doped amorphous silicon layer 108, thereby forming the lower electrodes 112 of various capacitors that are separated from each other. As shown in FIG. 1E, after removal of the PR layer 110, the silicon oxide layer 106 is recessed by performing a wet chemical etch process. Simultaneously, the remaining portion of the oxide layer 106 in the peripheral circuit region 122 is also removed. As shown in FIG. 1F, hemispherical silicon grains 114 are sequentially formed on the sidewalls of the lower electrodes 112. Hence, the exposed surface area of the lower electrodes 112 is increased. As shown in FIG. 1G, an ONO/NO dielectric layer 116 is formed over the lower electrodes 114 and the silicon nitride layer 102. Lastly, a conductive layer 118 is formed over the dielectric layer 116 to form the upper electrode of the capacitor, thereby completing the fabrication of a conventional crown-shaped DRAM capacitor.
As shown in FIG. 1G, there is a height difference of about 8000 xc3x85 to 10000 xc3x85 between the lower electrodes 112 in the crown-shaped capacitor region 120 and the silicon nitride layer 102 in the peripheral circuit region 122. Hence, planarizing the deposited upper electrode layer 118 and the peripheral circuit region 122 is difficult, and thereby produces a poor foundation for forming the desired devices in subsequent steps.
Accordingly, one object of the present invention is to provide a method of planarizing the peripheral circuit region of an advanced DRAM. Nitrogen is implanted into the silicon dioxide layer in the peripheral circuit region to form a silicon oxy-nitride layer. The silicon oxy-nitride layer serves as a protective layer shielding the silicon dioxide layer in the peripheral circuit region from the subsequent chemical-mechanical polishing and silicon oxide layer removal. The silicon oxy-nitride layer also forms a platform in the peripheral circuit production.
A second object of this invention is to provide a method of planarizing the peripheral circuit region of an advanced DRAM that can be easily implemented.
To achieve these and other advantages, and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of planarizing the peripheral circuit region of an advanced DRAM. By implanting nitrogen into a silicon dioxide layer to form a silicon oxy-nitride layer, the problem caused by the planarization of the peripheral circuit region is thus solved.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.